Electric discharge apparatus



Filed July 23 1952 Inve William cvvhite,

HIS Att y Aprifi 9, 1935.

ELECTRIC DISCHARGE APPARATUS Patented Apr. 9, 1935 PATENT OFFICE ELECTRIC DISCHARGE AI'PARATUS William C. White, Schenectady,

General Electric Company,

New York N. Y., assignor to a corporation of Application July 23, 1932, Serial No. 624,208

5 Claims.

The present invention relates to electric discharge apparatus and more particularly to large power tubes which utilize metal envelopes. The envelope usually contains a cathode, directly or indirectly heated, and there may be provided one or more additional electrodes between the cathode and envelope, also a gas or vapor which serves as the source of positive ions.

In order to evacuate a device of this character and to provide for sealing, it is customary to terminate the metal envelope in a glass portion and to extend the leads of the various electrodes through individual seals formed in the glass. The glass portion is joined to the metal envelope conveniently by a knife-edge seal.

A tube of this sort is adapted to operate as a rectifier, electrostatically controlled or uncontrolled, an amplifier or other form of electrical translation device. During operation, the tube attains a relatively high temperature and unless precautions are'taken to maintain the various seals cool, there is apt to be leakage which may destroy the tube.

It has been proposed heretofore to provide the necessary cooling efiect by means of a fan, also by immersing the tube in oil or other liquid but it is found that the additional apparatus required for this purpose is not only expensive and cumbersome but in some cases, is undependable. An object of the present invention is to provide an accessory of simple design which may be readily secured to and detached from the tube, and which provides a cooling efiect to all of the seals. In brief, my invention contemplates the use of a metal casing which surrounds the glass base of the tube, including the seals, and is secured in spaced relation to the metal portion of the envelope. One end of the casing extends below the glass envelope portion and is closed except for an opening through which cool air is caused to enter by convection eiiects of the heated air above. The casing thus provides a chimney effect and in addition, is adapted to serve as a base for the tube so as to support the latter in an upright position when being shipped or stored. Inasmuch as the casing entirely surrounds the glass portion of the envelope, it aifords substantial protection to the seal-off and glass parts. Tubes of this character usually employ mercury vapor as a source of positive ions, i. e. in order to neutralize space charge, and the excess mercury is carried in a protuberance formed integral with the lower portion of the glass envelope and communicating with the interior thereof. In accordance with my invention, the improved casing provides not only a cooling effect for the metal-to-glass seals but also serves to maintain the excess mercury contained in the glass protuberance at a relatively constant temperature regardless of the temperature of the device itself. My invention therefore provides a simple arrangement for maintaining the vapor pressure within the envelope constant. other objects and features will be apparent as the specification is perused in connection with the accompanying drawing in which Fig. 1 represents a longitudinal section in part, of a tube provided with the improved cooling accessory, and Fig. 2 is a cross-sectional view taken along the line 22 in Fig. 1.

In the drawing, numeral 5 designates a cylindrical metal envelope, of copper, iron or the like which terminates at the top in a handle-like extension 2, and at the bottom, is closed by a glass member 3 joined to the metal by a knife-edge or tapered seal. The envelope i contains an indirectly heated cathode of any appropriate design and is shown as being provided with one or more perforate heat shields 5 to which the flanged upright members 6 are riveted, also with a horizontal disk member 4 for shielding purposes. Four of the upright members are equidistantly spaced about the cathode and joined at the bottom to a metal collar '1 of somewhat larger diameter than the cathode. The collar l fits snugly about a reentrant glass member 8 which forms part of the terminating portion of the envelope. The cathode is provided with three equidistantly spaced leads 9, two of which are adapted to carry the load current, the remaining lead being connected to the heater (not shown) within the cathode. These leads are constituted of flexible cable, rigidly joined respectively to rod members l!) which pass through the glass portion of the envelope. In order to produce an hermetic seal about these rod members, the reentrant glass portion 8 is provided with downwardly-extending (as shown) glass tubular extensions I i which are terminated respectively at the end remote from the envelope by metal thimbles I2 to which the rod members H) are secured. Connections are made to these rod members by means of flexible cables i3 provided at the connection end with a metal cap it, as is well known in the art. The glass portion also carries a centrally disposed downwardly-extending glass tube or protuberance l5 which communicates with the interior of the envelope and contains a vapor-producing material such as mercury.

During operation, a portion of the mercury is vaporized to provide the necessary positive ions, and the remaining portion collects in the bottom of the tube l5 which is located at the coolest place on the device. It is well known that the temperature of the excess mercury determines for the most part, the vapor pressure within the. envelope and it is therefore desirable to maintain this body of mercury at a uniform temperature regardless of temperature variations found in the envelope proper.

In accordance with my invention, there is provided a casing l6, preferably of thin metal, and formed of any suitable configuration, for example, as sections havingdifferent diameters, with the largest diameter at the position farthest remote from the envelope. The casing at the smaller end is of slightly larger diameter than the envelope and is secured thereto at any position along the length of the envelope by means of four spacers I 8 of insulating material attached to the casing by screws I! to provide annular spaces between the casing and the envelope, as is shown more clearly in Fig. 2. The casing extends downwardly for a considerable distance beyond the glass envelope portion and is closed at the bottom, preferably by a transversely-extending plate I9 of fiber or other insulating material and secured to the casing in any suitable manner, for example'by screws 20. There isa central opening in the closure member l9 which supports an upwardly-extending cylinder 2| of fiber or other insulating material. The cylinder is of a diameter sufficiently large tosurround the protuberance IE but is small enough to permit insertion for a short distance into the interior of the reentrant member 8.

A device, such as described, is suitable for rectifying purposes and in operation, current is supplied to the heater of the cathode and a relatively high voltage applied between the cathode and the metal envelope which may serve as the anode. When operating, the tube is preferably suspended from the handle member 2 so that the bottom of the casing I6 is held at a considerable distance from the ground or floor. In order rigidly to maintain the tube in this position, it may be desirable to provide the handle member with a pair of openings 22 through which bolts can be passed and secured to a convenient support.

It is apparent that when the tube is suspended in this manner and the envelope has in normal operation attained an elevated temperature, relatively cool air is drawn naturally into the interior of the cylinder 2| through the opening in the base. This natural draft may be supplemented, if desired, by any suitable form of blower, although it has been found in practice that in most cases sufficient cooling effect can be obtained solely by convection. The air, however introduced, strikes the metal thimbles l2, and their seals, then has its direction reversed, as indicated by the arrows, and is caused to leave the casing at the annular spaces formed between the spacers l8. This cool air also flows past the central protuberance l5 and maintains the lower end of this member relatively cool and at a fairly constant temperature so that the vapor pressure within the envelope is maintained substantially constant regardless of changes in load conditions. The casing l6 thus provides a chimney effect in which a natural, or combined natural and forced draft of relatively cool air, is caused to flow past all of those surfaces such as the glass-to-metal seals, which require cooling. The effectiveness of the casing under these conditions, is so pronounced that even when only natural draft is employed,

the glass parts, including the seals, have been I found to run at much lower temperatures than in the absence of the casing and exposed directly to the surrounding air. The chimney effect may be enhanced, if desired, by extending the conduit 2| downwardly a sumcient distance to reach into a region of cool air which is entirely unaffected by radiation of heat from the envelope I. This extension, conveniently may form part of a supporting structure on which the tube rests, and hav- 1 ing the opening in the extension register with the opening in the conduit. It is further evident that the central position of the protuberance l5 within the conduit 2! lends itself to an accurate control of the temperature of the mercury condensate because the protuberance is subjected to.

serves conveniently as a base for the tube on Y which the latter can rest when it is not being used, also as a protection for the seal-on" and glass parts.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An electric discharge device comprising an envelope constituted of glass and metal portions sealed together and containing an electrode which cooperates with said metal portion to translate electrical energy, a leading-in conductor for said electrode, said glass envelope portion including a tubular member which extends away from the envelope, said member being closed by a metal thimble sealed thereto, said leading-in conductor being connected to said thimble, a casing surrounding the seal between the glass and metal portions in spaced relation and extending beyond the entire glass and metal envelope portions said casing being closed at its end remote from the envelope except for an opening through which air may be admitted, and caused to move by natural circulation past the seals between the thimble and the tubular member, also between the glass and metal envelope portions, and out through the space between the envelope and the casing.

2. An electric discharge device comprising an envelope constituted of glass and metal portions sealed together and containing an electrode which cooperates with said metal portion to translate electrical energy, a leading-in conductor for said electrode, a metal thimble sealed to the glass envelope portion and secured to said conductor, a casing surrounding one end of said metal envelope portion and secured thereto in spaced relation, said casing extending beyond the glass and metal envelope portions and terminating in a closed end except for a relatively small opening through which air may be caused to flow past all of said seals and out through the space between the envelope and the casing.

3. An electric discharge device comprising an envelope constituted of glass and metal portions sealed together and containing an electrode which cooperates with said metal portion to translate electrical energy, said glass envelope portion including a tubular member which extends away from the envelope, said member being closed at the bottom and containing a'vapor-yielding material, a casing surrounding one end of said metal envelope portion and secured thereto in spaced relation, said casing extending beyond the said tubular member and terminating in a closed end except for a small opening through which air may be caused to flow past the said material contained in the tubular member, also past the seal between the glass and metal envelope portions, and out through the space between the envelope and the casing.

4. An electric discharge device comprising an envelope constituted of glass and metal portions sealed together and containing an electrode which cooperates with said metal envelope portion to' translate electrical energy, a leading-in conductor for said electrode, said leading-in conductor being connected to a metal thimble which is sealed to the glass envelope portion, a casing surrounding one end of the metal envelope portion and secured thereto in spaced relation, said casing extending beyond the glass envelope portion and being closed at the end remote from the envelope by a member which contains a central opening, a tubular member secured to said member in line with said opening, said-tubular mem-' ber extending toward the envelope and terminating in the region of the seal between said also past the seal between the said glass and metal envelope portions, and out through the space between the envelope and casing.

5. An electric discharge device comprising an envelope constituted of glass and metal portions sealed together and containing an electrode which cooperates with said metal portion to translate electrical energy, said glass portion being constituted of a reentrant member containing a plurality of glass tubular members which extend in a direction away from the interior of the envelope, one of said tubular members being closed by a metal thimble sealed thereto, a leading-in conductor for said electrode, said leading-in conductor being secured to said thimble, another of said tubular members being closed at the bottom and containing a vapor-yielding material, a casing surrounding one end of the metal envelope portion and secured thereto in spaced relation, said casing extending beyond the glass envelope portion and terminating in a closed end except for a small opening through which air may be caused to flow past all of said tubular members, also past the seal between the said glass and metal envelope portions and out through the space between the envelope and the casing.

WILLIAM C. WHITE. 

